1. Field of the Invention
The present invention relates to a polymer for imparting high light resistance and weather resistance (hereinafter simply referred to as "light resistance") to fibers. The invention further relates to a highly light resistant fiber containing the polymer, to a highly light resistant fiber having a layer containing the polymer on its surface, and to a process for the production of the fibers.
2. Description of the Related Art
Polyurethane fibers are characterized by high elasticity and are widely used in numerous applications such as stockings, undergarments, as well as swimsuits, ski suits, and other sportswear, and elastic bandages, artificial vessels, and other medical articles. However, such polyurethane fibers are poor in light resistance. Specifically, by action of ultraviolet rays in sunlight or light from fluorescent lamps, the molecules of polyurethane fibers are photolyzed, and the strength and other properties of the fibers are deteriorated or dyed fibers are discolored.
Separately, polyester fibers are highly strong and highly elastic, are satisfactorily resistant to heat and chemicals, and are in wide use for clothing materials and industrial materials. The polyester fibers are more resistant to light and are therefore more resistant to light-induced deterioration and discoloring than polyurethane fibers and polyamide fibers. Demands on the use of such polyester fibers for interior members of cars and other materials have been increased, as such materials are often exposed to sunlight. However, higher light resistance is required as high grade cars are demanded. Improvements in light resistance of other fibers have been also demanded.
To improve light resistance, light resistance improving agents such as ultraviolet absorbents and antioxidants which are low molecular weight compounds are conventionally added to fibers (e.g., Japanese Unexamined Patent Application Publication No. 4-153316). Such light resistance improving agents are added to fibers by a process which comprises the step of coating surfaces of fibers with the light resistance improving agents after the formation of fibers (surface treatment process), or by a process which comprises the steps of adding the light resistance improving agents to a spinning material prior to a spinning process, and forming fibers from the resulting mixture (material adding process). However, according to the surface treatment process, the light resistance improving agents is readily peeled off from the fiber and a long-term improvement effect on light resistance cannot be significantly expected. In addition, the feeling of the resulting fibers is changed and high quality products cannot be obtained. In contrast, the material adding process is disadvantageous in that in wet spinning, for example, the light resistance improving agents is dissolved out into a coagulation bath, and only a portion of the added light resistance improving agents remains in the fiber. In addition, such a low molecular weight light resistance improving agents bleeds out on the surface of the fiber and, ultimately, is peeled out from the fiber, and the appearance of the fiber is deteriorated with time.